This invention relates in general to shift lever assemblies for transmissions, such as are commonly used in vehicular drive train systems. In particular, this invention relates to an improved structure for such a shift lever assembly that facilitates the adjustment of the amount of biasing force that is needed to move the shift lever when selecting various shift rail positions used in changing gear ratios in the transmission and reduces the amount of undesirable noise that is generated by the shift lever.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. The transmission of the engine/transmission assembly typically includes a case containing an input shaft, an output shaft, and a plurality of meshing gears. The meshing gears contained within the transmission case are of varying size so as to provide a plurality of gear ratios. By appropriately shifting among these various gear ratios, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner.
Many transmission structures are known in the art for shifting among these various gear ratios manually, i.e., in response to some physical exertion by the driver of the vehicle. In a conventional manual transmission, the driver grasps and moves an upper portion of a pivotable shift lever to effect shifting of the transmission. In response thereto, a lower portion of the shift lever engages and moves one of a plurality of shift rails provided within the transmission. The shift rails are typically supported within the transmission case for sliding movement from a central neutral position either forwardly to a first gear engaging position or rearwardly to a second gear engaging position. Thus, the initial selection and subsequent movement of a particular shift rail causes certain ones of the meshing gears to be connected between the input shaft and the output shaft. As a result, a desired gear ratio is provided between the input shaft and the output shaft.
Because of the interaction between the pivotable shift lever and the other components of the transmission, a certain amount of force is needed to move the shift lever between shift rail positions when changing gear ratios in the transmission. In order to accommodate the varying desires of different people who operate the transmission, it is desirable to be able to adjust the amount of force that is needed to move the shift lever between various shift rail positions when changing gear ratios in the transmission. This shift lever actuation force further may be responsive to a biasing force that is proportional thereto. This biasing force may further provide a return movement of the shift lever to a predetermined position relative to other transmission components. Additionally, it has been found that the transmission and other components of the drive train system generate noises and vibrations during operation. The shift lever can undesirably transmit these noises and vibrations to the area of the person who is operating the transmission. Thus, it would be desirable to provide an improved structure for a shift lever assembly that facilitates the adjustment of the amount of force that is needed to move the shift lever between various shift rail positions when changing gear ratios in the transmission. It would be further desirable to provide an improved shift lever assembly structure that reduces the amount of undesirable noise and vibration generated by the shift lever due to various excitation forces and structural resonances.